This invention relates to a device for detecting either a burned out lamp or malfunctioning lamp in a string of lights that are connected in series. It is particularly useful in detecting a burned out lamp or defective socket in a string of miniature low voltage holiday lights. It also relates to device that can function as a voltage detector for various applications. Throughout this document, the term non functioning lamp shall be deemed to mean that the lamp is not illuminated due to any of a number of reasons including but not limited to a defective or burned out lamp, or due to a defective socket or failure of the socket to make electrical contact with the lamp.
There are various types of miniature light strings or light sets. Examples of miniature lights and displays can be found in U.S. Pat. No. 5,453,664 to Harris, U.S. Pat. No. 5,624,181 to Miller et al. and U.S. Pat. No. 5,860,731 to Martinez. These strings of lights are often used during holiday times for decorative Christmas tree light strings. Other uses include framing a window with a series of miniature lights or wrapping a string of miniature holiday lights around a wreath that is in turn hung on a wall. The miniature light sets include a plurality of light sockets disposed along and electrically connected to an electrical wire or conductor. A miniature lamp is mounted in each socket. All of the lamps are connected in a series circuit.
In standard household applications, the voltage available is 120 volts A.C. For an extended length of lights, such as used on Christmas trees or other extended length applications, the miniature lamps are generally 2.4 volt incandescent lamps. So that the lamps will operate in this environment, a standard string of miniature lights has fifty lamps that are connected in series. Thus there is approximately a 2.4 volt drop across each lamp.
In another example there are one hundred lamps in a standard string. In this case the lamps are 1.2 volt incandescent lamps with approximately a 1.2 volt drop across each lamp.
The main problem with the string of holiday lights is detecting a burned out lamp in a series circuit. The problem is especially acute in the case of fifty or one hundred lamps connected in series where, if one lamp fails, or merely is removed or not making electrical contact with its socket, the entire string of lights go out unless there is a shunt integral with each lamp, to maintain the other lamps lit. The shunt keeps current running through the socket in the event that the lamp bums out. When this occurs, the voltage distributed among the remaining lamps is increased thus reducing the life of the remaining lamps in the string.
A problem that has not been solved by past devices is identifying a particular lamp that is burned out or not making electrical contact with its socket. If all of the lamps in a string are off, the user can""t readily identify which lamp is the non-functioning lamp. If the lamps have been carefully placed so as to make the effect look natural, it is even more difficult to find the non-functioning lamp. This is especially true for artificial factory wired Christmas trees. In the past the user had to check each lamp individually until the burned out lamp or lamp not properly making contact is found. Obviously, this is time consuming and frustrating for the user. In some instances, the user may become so frustrated that an entire string of lights may be discarded merely because the user couldn""t find the bad lamp or the user didn""t want to spend the time looking for it.
In another application, a light emitting diode (xe2x80x9cLEDxe2x80x9d) is commonly used to indicate when a circuit is energized. For example many household appliances use LED""s to indicate that a feature is xe2x80x9conxe2x80x9d. LED""s are relatively expensive compared to small resistors. Thus if a resistor can replace the LED, a cost savings results. Still another application allows a voltage detection device, which may be a resistor, in place of the LED""s, neon lamps, or small incandescent lamps. Throughout this application, the term xe2x80x9cLED""sxe2x80x9d shall include light emitting diodes, neon lamps or small incandescent lamps.
Thus it is an object of the invention to provide a visual indication to alert the user of a string of holiday lights as to which lamp is either burned out or non-functioning.
It is a related object to provide an electroluminescent indicator that is connected in parallel with each of the holiday lights in a string and illuminates when the lamp with which it is connected in parallel bums out or malfunctions. It is another object to provide a resistor in parallel with each of the holiday lights that heats up above a predetermined level when the lamp with which it is in parallel bums out or malfunctions. A related object is to paint the resistor with thermochromic paint or temperature sensitive liquid crystal paint so that as it heats up it gives a visual indication when the lamp with which it is connected in parallel bums out or malfunctions.
Yet another object is to provide a material that is impregnated with a scent that is released when heated above a predetermined temperature, which occurs when the lamp bums out or malfunctions. Still another object is to provide an audible alarm when a lamp burns out or malfunctions.
An advantage of giving the user an indication of the lamp that has burned out or malfunctioned is that it enables the user to quickly locate and replace the defective lamp or socket.
Another object is to use a voltage detection device in place of other detection means such as light emitting diodes, neon lamps, or small incandescent lamps, to indicate the status of components in an electrical circuit.
Applicant""s invention is a device that solves the problem of locating defective lamps or sockets by alerting the user which lamp is not functioning. Applicant""s device connects a signal indicating means in parallel with each lamp. When the lamp is not functioning, the rest of the lamps in the series circuit go off. The full line voltage then appears across the signal indicating means causing a visual signal, alarm sound or odor to be emitted directing the user to the non functioning lamp. Examples of signal indicating means are an electroluminescent indicator, a resistor coated with thermochromic paint or temperature sensitive liquid crystal paint, impregnating the socket with a material that emits an odor when heated, and an alarm sounding device that activates when the voltage increases to a predetermined level. If more than one lamp is not functioning, the signal indicating means can still operate as long as the voltage is sufficient to trigger the signal indicating means.
Applicant""s device can further be adapted as a voltage detector to indicate when a circuit is energized. For example, in an appliance heater circuit, the voltage passing through a resistor in parallel with the heating circuit can indicate the status of the circuit without the need to use LED""s.